Radiant heat collective adapter and group adapter

Abstract

The present disclosure relates to radiative heat collective bonders and group bonders for packaging semiconductor die stacks. The bonder typically includes: a shield that is positioned at least partially around the die stack; and a radiative heat source that is positioned inside the shield and configured to emit a radiative heat flux in a direction away from the shield. The bonder may further include a bonding head configured to contact the back side of the topmost die of the die stack and optionally include another bonding head configured to contact the substrate below the die stack. The radiative heat source may be configured to direct the radiative heat flux to at least a portion of the die stack to reduce the vertical temperature gradient in the die stack. One or both of the bonding heads may be configured to concurrently direct a conductive heat flux into the die stack.

Description

Technical Field

[0001] The present disclosure relates generally to bonded semiconductor devices and, in several embodiments, more particularly to systems and methods for thermocompressive collective bonding and group bonding of semiconductor dies. Background Art

[0002] Microelectronic devices, such as memory devices, microprocessors, and light emitting diodes, typically include one or more semiconductor dies mounted to a substrate and wrapped in a protective covering. The semiconductor die includes functional features, such as memory cells, processor circuits, interconnect circuit systems, and the like. Semiconductor die manufacturers are under increasing pressure to reduce the volume occupied by the semiconductor die while increasing the capacity and / or speed of the resulting encapsulated assembly. In order to meet these demands, semiconductor die manufacturers often stack multiple semiconductor dies vertically one above the other to increase the capacity or performance of microelectronic devices within a limited volume on a circuit board or other element to which the semiconductor die is mounted. The stack can be bonded together using a bonding material. For such vertically stacked semiconductor dies, through-silicon vias (TSVs) are often used. These TSVs on adjacent semiconductor dies are typically electrically connected to each other using direct physical coupling, with the bonding pads of one die directly bonded to the bonding pads of another die. Summary of the invention

[0003] On the one hand, the present disclosure relates to a semiconductor die stack bonding tool, comprising: a first bonding head coupled to a first handle and configured to contact the back side of a topmost die in a die stack formed on a substrate; a shield positioned adjacent to the bonding head, the shield having a sidewall with a first inner surface facing the bonding head; and a radiant heat source positioned inside the first inner surface to selectively emit a radiant heat flux in a direction away from the first inner surface, wherein the radiant heat source is configured to direct the radiant heat flux to at least a portion of the die stack to reduce a vertical temperature gradient in the die stack.

[0004] On the other hand, the present disclosure relates to a semiconductor die stack bonding tool, comprising: a first bonding head coupled to a first handle and configured to contact the back side of a topmost die in a die stack formed on a substrate; a second bonding head coupled to a second handle and configured to contact the substrate below the die stack; a shield positioned adjacent to the first bonding head, the shield having a sidewall with a first inner surface facing the first bonding head; and a radiant heat source positioned inside the first inner surface to selectively emit a radiant heat flux, wherein the first and second bonding heads are configured to apply relative compressive pressures to the die stack and the radiant heat source is configured to concurrently direct the radiant heat flux to at least a portion of the die stack to group bond the die stack.

[0005] In a further aspect, the present disclosure relates to a method for collectively bonding or group bonding semiconductor dies using a semiconductor die stack bonding tool, the method comprising: positioning the bonding tool above an adhered semiconductor die stack; lowering the bonding tool so that the first bonding head contacts the back side of the topmost die of the die stack and the shield at least partially laterally surrounds the die stack; applying a radiant heat flux to the die stack to melt solder positioned between interconnects and form electrical connections between the dies in the die stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is an enlarged cross-sectional view showing a semiconductor device and a thermocompression group bonder configured according to an embodiment of the present technology.

[0007] Figure 2 is an enlarged cross-sectional view showing a semiconductor device and a thermocompression group bonder configured according to another embodiment of the present technology. DETAILED DESCRIPTION

[0008] The technology disclosed herein relates to semiconductor devices, systems having semiconductor devices, and related methods for manufacturing semiconductor devices. The term "semiconductor device" generally refers to a solid-state device that includes one or more semiconductor materials. Examples of semiconductor devices include logic devices, memory devices, and diodes, among others. In addition, the term "semiconductor device" may refer to a finished device or an assembly or other structure at various processing stages before becoming a finished device.

[0009] Depending on the context in which it is used, the term "substrate" may refer to a structure that supports an electronic component (e.g., a die), such as a wafer-level substrate or a single, die-level substrate or another die for die stacking applications. One of ordinary skill in the relevant art will recognize that appropriate steps of the methods described herein may be performed at the wafer level or at the die level. In addition, unless the context indicates otherwise, conventional semiconductor manufacturing techniques may be used to form the structures disclosed herein. For example, materials may be deposited using chemical vapor deposition, physical vapor deposition, atomic layer deposition, spin coating, electroplating, and / or other suitable techniques. Similarly, materials may be removed, for example, using plasma etching, wet etching, chemical mechanical planarization, or other suitable techniques.

[0010] The term "bonding head" may refer to an upper / lower chuck, tip, or tool used to mount a semiconductor die to a substrate. Such a bonding head may be capable of applying heat and / or pressure to a semiconductor die or die stack. A person of ordinary skill in the relevant art will understand that the technology may have additional embodiments and may be used without reference below. Figure 1 and 2The techniques are practiced in the context of several details of the described embodiments, and suitable steps of the methods described herein may be performed at the wafer level or at the die level.

[0011] The term "shield" may refer to a thermally insulating and / or reflective shield configured to at least partially surround one or more semiconductor die stacks during group bonding. The descriptions and illustrations of the shapes and configurations of the group bonder heat shield herein are exemplary and should not be construed as limiting the scope of the present disclosure. In this regard, in several embodiments, the shape of the group bonder heat shield is any shape or configuration suitable for sufficiently limiting heat transfer to components outside the group bonder shield and / or reflecting thermal energy from a heat source to a desired area within the group bonder shield.

[0012] In several embodiments, a semiconductor die includes at least one contact (e.g., a bond pad or a portion of a TSV extending through the die) exposed on the front or back side of the die. In these embodiments, an interconnect structure is electrically coupled by bonding to the contact to allow electrical connections to be made with other components of the semiconductor device using solder or other conductive structures.

[0013] Thermal compression bonding (TCB) may be used to bond semiconductor dies to a substrate or another semiconductor device individually or in groups, such as by sequential bonding, collective bonding, group bonding, etc. Sequential bonding generally involves bonding a single semiconductor die per cycle and includes holding a representative semiconductor die against a bond head using a tuned temperature and pressure profile to apply heat and pressure to the back side of the die such that heat from the bond head transfers through the die to sufficiently heat the solder to form an electrical connection between an interconnect structure on the back side of the die and a bonding surface of a substrate, die, device, etc. Sequential bonding includes repeating this process for each die in a stack of dies until the stack is formed (e.g., "2H" for a 2-die high stack, "4H" for a 4-die high stack, "8H" for an 8-die high stack, etc.).

[0014] Collective bonding typically includes bonding the die stack to a substrate by first "quickly attaching" the semiconductor die in a stacked position and then applying heat and pressure to the semiconductor die stack. During quick attach, the temperature and pressure applied to each die are low and only sufficient to flow the non-conductive film (NCF) laminated on the pillar side of the die. The quick attach of the die does not complete the electrical connector, and a final collective bonding step is performed, in which heat and pressure are applied to the entire stack from the top and / or bottom of the stack by a bonding head to flow the solder and collectively bond the die. In the example of an 8H stack, all 8 dies may be quick attached and then collectively bonded, or 7 of the dies may be quick attached and then collectively bonded by the eighth die (i.e., the top die). Both quick attach and collective bonding steps may be performed using the same tool or by any number of tools. Although collective bonding may increase efficiency compared to sequential bonding, each of these processes is relatively inefficient compared to group bonding.

[0015] The process of hot compression group bonding can be used to bond multiple die stacks at the same time and increase efficiency through sequential and collective bonding. In the group bonding process, multiple die stacks are quickly adhered to the appropriate position. Inside the group bonder, a handle with a bonding head contacts the back side of the top die above the stack and in some embodiments, a second handle with a bonding head is positioned below the die stack below the substrate or device. The bonding head can apply heat to the top and / or bottom of the die stack using conductive heating (e.g., heat conduction from the handle to the bonding head, or using a piezoelectric heater in the bonding head and other suitable heat sources). In this regard, the upper and lower bonding heads apply heat directed toward each other from the top and bottom dies of the stack to heat each of the interconnects within the die stack. The interconnects must be heated until the solder at each connector reaches the solid phase point, where the solder flows to form electrical and mechanical connectors between the dies in the stack. During the group bonding process, the bonding head can also apply relative compressive pressure to produce the desired bond line thickness (BLT) between the dies. The bond head may be formed of suitable materials to withstand the temperature, pressure, and cycles of the mass bonding process, such as ceramic materials with heat resistant polymer covers, among other materials. In other embodiments, the mass bonding process is performed without a lower bond head, and instead the substrate or wafer to which the die is bonded is located on a stage or other platform with or without heat.

[0016] The TCB process is performed at high temperatures to ensure that the bonding material reaches the desired internal temperature to reliably form interconnects, and as more die are assembled in a high-density die stack for group bonding (e.g., 4, 6, 8 or more die in a stack), higher temperatures are required to produce interconnect bonds due to temperature gradients. During group bonding of die stacks using conventional group bonding techniques, large temperature gradients may occur due to the conductive heat transfer rate from the upper and lower bonding heads through the substrate and die stack and due to the low thermal conductivity of the NCF. Therefore, before the stack reaches vertical temperature equilibrium, the temperature of the die closest to the bonding head may be higher than the die near the center of the die stack. Conventional group bonding processes are typically not long enough for this equilibrium to occur because the solder near the top and bottom die typically reaches the solid phase faster than the temperature rise at the vertical center of the die stack. Thus, the temperature required to melt and flow the bonding material at the vertical center of the stack at the bonding head may be significantly higher than the solid phase point, which may result in inconsistent BLT through the die stack, untreated sites of oxidation, and / or damage to other nearby components. Potential damage caused by high temperatures limits the number of dies that can be group-bonded in a die stack using conventional processes. Embodiments of the present technology reduce potential damage by applying heat to the die stack in a manner that reduces the temperature gradient across the height of the die stack so that lower temperatures can be applied to the top and bottom of the die stack to create interconnect bonds. The shields disclosed herein can also be configured to shield surrounding components during the thermal compression group bonding process.

[0017] In embodiments of the present technology, a radiant heat source is applied in addition to or in lieu of conductive heating in a bond head during thermocompression group bonding. The radiant heat source may be configured to apply a radiant heat flux (e.g., by a heat lamp emitting electromagnetic radiation, such as a light emitting diode (LED) or an incandescent lamp emitting infrared (IR), ultraviolet (UV), etc.) to an area of ​​the die stack (e.g., from the side) to flow solder and form electrical connections, and / or reduce vertical temperature gradients caused by conductive heating from the bond head. Conductive heat from the bond head may optionally be omitted so that radiant heat is the only heat source during group bonding, or radiant heat may be used in combination with heat from the bond head.

[0018] The radiant heat source may be applied in conjunction with a shield configured to at least partially surround one or more semiconductor die stacks during group bonding. The shield may be configured to insulate components outside the shield from heat generated by the bond head and / or radiant heat lamps. The shield may also have an inner surface configured to reflect radiation from the heat lamps, thereby producing more uniform stack heating, and / or distributing heat to areas of the die stack that are not aligned with direct radiant heating, as will be explained in more detail below.

[0019] In addition to other advantages over conventional techniques, the radiant heat source process described herein may also provide improved throughput; improved die stack reliability by reducing solder non-wetting, cold soldering, open interconnects, defects, or higher resistance interconnects; extended equipment and bonding head life; lower operating costs; and higher population bonding process capabilities. In addition, the application of radiant heat to the die stack can be more reliably controlled compared to conductive heating, and the reflective shield can improve the uniformity of the heat applied to the die stack. Configurations of the present technology may be described herein with reference to TSV and / or three-dimensional integration (3DI); however, the present technology is also applicable to other interconnect types, including flip chip bonding (FC), direct chip attachment (DCA), and D2S, among others. The description of the present technology in conjunction with a specific configuration should not be construed as limiting the application of the present technology.

[0020] Figure 1 is an enlarged cross-sectional view showing a semiconductor device configured in accordance with an embodiment of the present technology and a thermocompression cluster bonder assembly 100. The cluster bonder assembly 100 is shown positioned in contact with a stack of dies of semiconductor devices and forming electrical connections between contacts on each die and the semiconductor devices. Figure 1 The semiconductor device of FIG. 1 includes an example of a previously processed die stack 102 that is mechanically and electrically coupled to a substrate 108. The die stack 102 is shown after the group bonding process of the present technique has been performed, which forms electrical connections and sets a BLT between each die in the die stack 102. Figure 1 The semiconductor device also includes an unprocessed site having a trace 104 and a solder portion 106, configured to receive a die stack in a subsequent group bonding process. The configuration of the semiconductor device in the figure is only a single example and is not intended to limit the semiconductor device to the illustrated configuration. In other embodiments, the semiconductor device has any suitable component configuration.

[0021] The group bonder assembly 100 may include a first upper bonding head 110 fixed to an upper handle 112, and a second lower bonding head 114 fixed to a lower handle 116. The upper bonding head 110 and the upper handle 112 may be configured to apply heat and / or pressure to the uppermost semiconductor die through the upper bonding head 110 to promote group bonding of the die stack 140. An exemplary die stack 140 for group bonding may include a first die 150, a second die 152, a third die 154, a fourth die 156, and a fifth die 158; however, the group bonding process described herein is applicable to any number of dies in the stack. The first die 150 may be the lowermost die, the fifth die 158 may be the uppermost die, and the dies 152, 154, and 156 may be the middle dies. As shown, the die stack 140 is stacked on top of the trace 104 of the substrate 108 so that the lowermost die 150 contacts the trace 104. Each of the first, second, third, and fourth dies 150, 152, 154, and 156 in the die stack 140 has both a lower conductive interconnect 142 extending from the front side of the die, and an upper interconnect 144 (e.g., TSV, pillars on bonding pads, etc.) extending from the back side of the die. The fifth die 158 has only a lower conductive interconnect 142 extending from the back side of the die 158. Each of the conductive interconnects 142 and 144 forms an electrical connection between the substrate 108 and the dies 150 to 158. The interconnects 142 and 144 may be electrically coupled with solder 146, which melts and flows during the group bonding process.

[0022] Upper bond head 110 may transfer conductive heat flux 190 into uppermost die 158 of die stack 140 such that heat flux 190 travels through the components of die stack 140 toward lower bond head 114. Lower bond head 114 and lower handle 116 may be configured to apply heat and / or pressure into substrate 108 through lower bond head 114 to transfer conductive heat flux 192 into substrate 108 such that heat flux 192 travels through substrate 108, into traces 104, and through the components of die stack 140 toward upper bond head 110. Heat fluxes 190 and 192 have heat transfer rates determined by the temperature of bond heads 110 and 114, and the thermal conductivities of the materials used in substrate 108 and die stack 140. Thus, during group bonding of the die stack 140 , there may be some vertical temperature gradient within the die stack 140 , generally governed by Fourier's law, causing the middle point among the middle dies 152 , 154 , and 156 to have the lowest rate of temperature increase within the die stack 140 .

[0023] The group bonder assembly 100 may include a shield or shield assembly 120 configured to at least partially surround a die stack to be processed by the group bonder assembly 100. The shield assembly 120 includes sidewalls 122, an upper wall 124, and an opening 130 through which the upper handle 112 passes. The lower end of the shield assembly 120 may be open and configured to allow the shield assembly 120 to be placed on a die stack 140 for a group bonding process. The sidewalls 122 and upper wall 124 may be configured to insulate heat generated within the shield assembly 120, which may provide more predictable temperatures to improve control within the shield assembly 120 and protect adjacent components, such as the die stack 102 and traces 104 at unprocessed sites. As described above, the sidewalls 122 may include radiation reflective sidewall surfaces 126 facing the upper bond head 110 and / or the die stack 140, and the upper wall 124 may include radiation reflective upper wall surfaces 128 facing the upper bond head 110 and / or the die stack 140, each surface having a radiation reflectivity. The reflective surfaces 126 and 128 are configured to reflect radiant heat generated within the shield assembly 120 toward the die stack 140 to reduce vertical temperature gradients in the middle dies 152, 154, and 156. In some embodiments, one or more fins, dividers, and / or compartments (not shown) may be positioned within the shield assembly 120 to shield areas where high temperatures are not desired, or to direct heat to areas for more uniform heating of the die stack 140.

[0024] One or more radiant heating elements 132 may be positioned within the shield assembly 120 to provide additional heating of the die stack 140 during the group bonding process. The radiant heating elements 132 selectively transfer radiant heat flux 194 into the die stack 140. Figure 11, the radiant heating elements 132 are generally positioned to the die sides of the die stack 140 near the sidewalls 122 and are configured to direct the radiant heat flux 194 to the sides of the die stack 140. For example, the radiant heating elements 132 may be configured to direct the radiant heat flux 194 to areas of the die stack 140 where vertical temperature gradients will be greatest, i.e., along the middle dies 152, 154, and 156 between the upper and lower dies 110 and 114. The radiant heat flux 194 may reduce the vertical temperature gradient in the die stack 140 by more uniformly heating the middle areas of the die stack 140 farthest from the upper and lower bond heads 110 and 114. In this regard, the radiant heating elements 132 may directly transfer the radiant heat flux 194 into components of the die stack 140, or may have portions of the radiant heat flux 194 reflected from the reflective sidewall surfaces 126 and the reflective upper wall surface 128 and into components of the die stack 140. In other embodiments, the shield assembly 120 itself may be heated to apply a conductive heat flux to the die stack 140. In some embodiments, the heat fluxes 190 and 192 are omitted from the upper and lower bond heads 110 and 114 so that only the radiative heat flux 194 is applied to the die stack 140.

[0025] Figure 2 1 is an enlarged cross-sectional view showing a semiconductor device and a hot pressing group bonder assembly 200 configured according to another embodiment of the present technology. Group bonder assembly 200 is similar to group bonder assembly 100, except that the position of the radiation heat source is different. Group bonder assembly 200 includes a shield assembly 220 configured to at least partially surround a die stack to be processed by group bonder assembly 200. Shield assembly 220 includes sidewalls 222, upper wall 224 and handle opening 230, and upper handle 112 passes through the handle opening 230. The lower end of shield assembly 220 can be open and configured to allow shield assembly 220 to be placed above die stack 140 for group bonding process. Sidewall 222 can include reflective sidewall surface 226, and upper wall 224 can include reflective upper wall surface 228, each surface having a reflectivity. Reflective surfaces 226 and 228 are configured to reflect the radiant heat generated in shield assembly 220.

[0026] The group bonder assembly 200 includes one or more radiant heating elements 232 positioned within the shield assembly 220 to provide additional heating of the die stack 140 during the group bonding process. Figure 2In the illustrated embodiment of FIG, the radiant heating element 232 is typically positioned above the die stack 140 and to the side of the upper bonding head 110 and the upper handle 112. The radiant heating element 232 emits the radiant heat flux 294 within the shield assembly 220 to provide additional heat into the die stack 140 to reduce the vertical temperature gradient. Since the radiant heating element 232 of the group bonder assembly 200 is typically not positioned to the side of the die stack 140, the radiant heat flux 294 can be reflected from the reflective sidewall surface 226 and the reflective upper wall surface 228 to direct the radiant heat flux 294 toward the die stack 140. In some configurations, the die stack 140 has a relatively short height compared to some radiant heat sources, so that only a single radiant heat source or only some radiant heat sources can be positioned to the side of the die stack based on physical size.

[0027] In the plan view of the illustrated embodiment, shield assemblies 120 and 220 may have a square, rectangular, geometric or arched shape, as well as other suitable shapes. In further embodiments, shield assemblies 120 and 220 may be sized and configured to surround multiple die stacks for simultaneous group bonding. In these embodiments, additional upper and lower bonding heads and handles are appropriately added to the group bonder assembly to group bond more than one die stack in the shield. In some embodiments, the shield assembly is fixed to the upper handle of the group bonder so that the shield assembly moves with the handle. In other embodiments, the shield assembly can be moved relative to the upper bonding head and handle and moved separately during the group bonding process so that the shield assembly can accommodate the group bonding of die stacks with multiple heights.

[0028] The present disclosure is not intended to be exhaustive or to limit the present technology to the precise form disclosed herein. Although specific embodiments are disclosed herein for illustrative purposes, various equivalent modifications may be made without departing from the present technology, as will be recognized by those skilled in the relevant art. For example, although the specification focuses on thermocompression bonding with NCF, NCP and / or WLUF, the present technology may also be applied to other processes and / or applications, such as flux and flip chips for microbump formation. In some cases, well-known structures and functions are not shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present technology. Although the steps of the method may be presented in a specific order herein, alternative embodiments may perform the steps in a different order. Similarly, certain aspects of the present technology disclosed in the context of a specific embodiment may be combined or eliminated in other embodiments. In addition, although the advantages that may be associated with certain embodiments of the present technology are disclosed in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments necessarily exhibit such advantages or other advantages disclosed herein fall within the scope of the present technology. Therefore, the present disclosure and associated technologies may cover other embodiments that are not explicitly shown or described herein.

[0029] As used herein, the terms "vertical", "lateral", "upper", and "lower" may refer to the relative direction or position of a feature in a semiconductor device in view of the orientation shown in the figure. For example, "upper" or "uppermost" may refer to a feature that is positioned closer to the top of the page than another feature. However, these terms should be broadly interpreted to include semiconductor devices with other orientations, such as inverted or tilted orientations, where top / bottom, above / below, above / below, up / down, left / right, and distal / proximal may be interchanged depending on the orientation. In addition, for ease of reference, the same reference numerals are used to identify similar or similar components or features throughout the present disclosure, but the use of the same reference numerals does not imply that the features should be interpreted as the same. In fact, in many of the examples described herein, the same numbered features have multiple embodiments that differ from each other in structure and / or function. In addition, the same shading may be used to indicate similarly synthesizable materials in a cross-section, but the use of the same shading does not imply that the materials should be interpreted as the same unless specifically described herein.

[0030] The present disclosure may also refer to quantities and numbers. Unless specifically stated, such quantities and numbers should not be considered restrictive, but should be considered as examples of possible quantities or numbers associated with the new technology. Moreover, in this regard, the present disclosure may use the term "multiple" to refer to quantities or numbers. In this regard, the term "multiple" means any number more than one, such as two, three, four, five, etc. For the purposes of the present disclosure, the phrase "at least one of A, B, and C" for example represents an average value (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible arrangements when listing more than three elements.

[0031] Based on the foregoing, it will be understood that specific embodiments of the new technology have been described herein for illustrative purposes, but various modifications may be made without departing from the present disclosure. Therefore, the present invention is not limited except for the appended claims. In addition, certain aspects of the new technology described in the context of a specific embodiment may also be combined or eliminated in other embodiments. In addition, although the advantages associated with certain embodiments of the new technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages and not all embodiments necessarily exhibit such advantages and fall within the scope of the present disclosure. Therefore, the present disclosure and associated technology may cover other embodiments that are not explicitly shown or described herein.

Claims

1. A semiconductor die stacking bonding tool, comprising: a bond head coupled to the handle and configured to contact a backside of a topmost die in a stack of dies formed on the substrate; a shield positioned adjacent the bond head, the shield having side walls and an upper wall, the side walls with a first radiation reflective inner surface facing the bond head; and a radiant heat source positioned above the bond head and at a first portion of the first radiation reflecting inner surface to selectively emit a radiant heat flux in a direction away from the first portion of the first radiation reflecting inner surface toward a second portion of the first radiation reflecting inner surface so that the radiant heat flux is reflected from the second portion of the first radiation reflecting inner surface to at least a portion of the die stack to reduce a vertical temperature gradient in the die stack. 2 . The semiconductor die stack bonding tool of claim 1 , wherein the bond head applies a conductive heat flux to the topmost die in the die stack.

3. The semiconductor die stack bonding tool of claim 1 , wherein the bonding head comprises a first bonding head, the shield comprises a first shield, and wherein the semiconductor die stack bonding tool further comprises a second A bond head is coupled to a second handle and configured to contact the substrate, the second bond head being vertically aligned with the first bond head and positioned on a side of the substrate opposite the die stack.

4. The semiconductor die stack bonding tool of claim 3 , wherein the first bond head applies a first conductive heat flux to the topmost die in the die stack, and wherein the second bond head applies a second conductive heat flux to the substrate toward a bottom of the die stack. 5 . The semiconductor die stack bonding tool of claim 1 , wherein the upper wall has an opening through which the handle passes.

6. The semiconductor die stack bonding tool of claim 1 , wherein the upper wall has a second radiation reflecting inner surface positioned above and facing the bonding head, and the radiant heat flux flows to the portion of the die stack by reflecting from the second radiation reflecting inner surface. 7 . The semiconductor die stack bonding tool of claim 1 , wherein an additional radiant heat source is positioned directly to the side of the die stack during collective bonding or group bonding such that additional radiant heat flux flows directly to the portion of the die stack. 8 . The semiconductor die stack bonding tool of claim 5 , wherein the handle is coupled to the upper wall such that the shield is configured to move with the handle.

9. A semiconductor die stacking bonding tool, comprising: a first bond head coupled to the first handle and configured to contact a backside of a topmost die in a stack of dies formed on a substrate; a second bond head coupled to a second handle and configured to contact the substrate beneath the die stack; a shield positioned adjacent to the first bond head, the shield having a sidewall with a radiation reflective inner surface facing the first bond head; and a radiant heat source positioned above the first engagement head and at a first portion of the radiation reflecting inner surface to selectively emit a radiant heat flux in a direction toward a second portion of the radiation reflecting inner surface, wherein the first bond head and the second bond head are configured to apply relative compressive pressures to the die stack, and wherein the radiant heat source is configured to concurrently direct the radiant heat flux to the second portion of the radiation reflective inner surface such that the radiant heat flux flows to at least a portion of the die stack by reflecting from the second portion of the radiation reflective inner surface.

10. The semiconductor die stack bonding tool of claim 9, wherein the first bond head applies a first conductive heat flux to the topmost die in the die stack, and wherein the second bond head applies a second conductive heat flux to the substrate toward the die stack. 11 . The semiconductor die stack bonding tool of claim 9 , wherein the shield further comprises an upper wall having an opening, the first handle passing through the opening during group bonding of the die stack. 12 . The semiconductor die stack bonding tool of claim 11 , wherein the radiation reflective inner surface is a first radiation reflective inner surface, and wherein the upper wall has a second radiation reflective inner surface positioned above and facing the first bond head. 13 . The semiconductor die stack bonding tool of claim 12 , wherein the radiant heat flux flows to the portion of the die stack by reflecting from the second radiation reflecting inner surface.

14. The semiconductor die stack bonding tool according to claim 9 further comprises a second radiant heat source, which is positioned to the side of the die stack and is configured to selectively emit a second radiant heat flux to at least a portion of the die stack in a direction away from the radiation reflecting inner surface to reduce the vertical temperature gradient in the die stack. 15 . The semiconductor die stack bonding tool of claim 11 , wherein the first handle is coupled to the upper wall such that the shield is configured to move with the first handle during the group bonding.

16. A semiconductor die stacking bonding tool, comprising: a bond head coupled to the handle and configured to contact a backside of a topmost die in a stack of dies formed on the substrate; a shield positioned adjacent to the bond head, the shield having side walls with a first radiation reflective inner surface facing the bond head and an upper wall having a second radiation reflective inner surface positioned above the bond head and facing the bond head; and a radiant heat source positioned in lateral alignment with or above the bond head and at a first portion of the first radiation reflecting inner surface to selectively emit a radiant heat flux in a direction away from the first portion of the first radiation reflecting inner surface toward the second radiation reflecting inner surface such that the radiant heat flux is reflected from the second radiation reflecting inner surface and the second portion of the first radiation reflecting inner surface to at least a portion of the die stack to reduce a vertical temperature gradient in the die stack. 17 . The semiconductor die stack bonding tool of claim 16 , wherein the bond head applies a conductive heat flux to the topmost die in the die stack.

18. The semiconductor die stack bonding tool of claim 16, wherein the bonding head comprises a first bonding head, the shield comprises a first shield, and wherein the semiconductor die stack bonding tool further comprises a second bonding head coupled to a second handle and configured to contact the substrate, the second bonding head being vertically aligned with the first bonding head and positioned on a side of the substrate opposite to the die stack.

19. The semiconductor die stack bonding tool of claim 18, wherein the first bond head applies a first conductive heat flux to the topmost die in the die stack, and wherein the second bond head applies a second conductive heat flux to the substrate toward a bottom of the die stack. 20 . The semiconductor die stack bonding tool of claim 16 , wherein the upper wall has an opening through which the handle passes.

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